With the prospect of Bolton appearing as a witness in the trial unresolved—it’s still possible he might not be called—several House Democrats on Monday initiated talks within their caucus about taking the dramatic step of subpoenaing him or once again requesting that he testify before a House committee, according to multiple Democratic sources. Bolton would, under oath, presumably say that Trump informed him at the time that he was leaning on Zelensky by withholding the $391 million in military assistance Ukraine needed for its ongoing war against Russia.

But, according to these same sources, Rep. Adam Schiff (D-Calif.), the chair of the House intelligence committee and the lead House impeachment manager, is not in favor of this, believing that Senate Republicans might somehow use such a move as an argument against calling Bolton as a witness in the impeachment trial. “The onus is clearly on the Senate to call a relevant and willing witness before they vote,” says a Democratic aide working on the impeachment trial.

Several House Democrats raising the idea of calling Bolton to testify in the House note they are sensitive to this, but they say they still intend to raise the matter within the Democratic caucus. They point out that a Bolton appearance in the House—or his refusal to testify—could put pressure on Senate Republicans to call him as a witness in the Senate trial.